This invention relates to composite propellants and more particularly to composite propellants having additives which do not migrate.
Numerous additives are used in solid rocket propellants to improve their burning rate, stability, sensitivity, and mechanical properties. Often the greatest influence on these factors are shown by low molecular weight materials which unfortunately cannot be used because their volatility results in partial or complete evaporation during curing or long term storage. Even if the vapor pressure of conventional additives is low enough, their migration within the propellant matrix often cannot be prevented, and "bleeding-out" of the additives and deterioration of the propellant's properties occur; e.g., compounds such as Hycat 6 and other alkyl ferrocenes increase the burning rate of propellants and have low vapor pressure but cannot be used as additives because they migrate to the surface of the solid propellant. Such migration causes increased sensitivity and erratic burning.
Ferrocene compounds increase the shock sensitivity of propellants. Migration to the surface of the propellant by the ferrocene causes the surface of the propellant to be even more shock sensitive than the average propellant would be before migration took place. Migration further destroys propellant homogeneity and permits higher burning rates on the surface of the propellant than throughout the remainder of the propellant, which is undesirable due to the unpredictability of the burning rate which in turn renders the rocket performance unpredictable.
The term Hycat 6 refers to an alkyl ferrocene compound available from Arapahoe Company of Boulder, Colo., a division of Syntex Company.
Many of the solutions proposed in the past do not solve the problem of additive migration. Other additives designed to reduce migration produce other problems, without solving the migration problem completely. With special attention directed to the ferrocenyl compounds as burning rate additives, several problems are generated. Ferrocenyl compounds are well-known burning rate additives. Low molecular weight ferrocene compounds vaporize out of the propellant. High molecular weight liquid ferrocene compounds also migrate to the surface of the propellant destroying the homogeneity of the propellant. Solid ferrocene compounds often sublime out of the solid propellant. Thus it is difficult to use ferrocene compounds as burning rate modifiers.
Accordingly, it would be desirable to provide a stable additive for use in propellants which will not compromise other desired properties of the propellant. Such an additive would be required to have a certain stability which is imparted to the propellant to which it is added.